Enthalpy and solubility data of CO2 in water and NaCl(aq) at conditions of interest for geological sequestration

The transfer of acid gases in saline aquifers under high pressures is an important step in their geological storage. The dissolution of carbon dioxide in water and in aqueous solution of sodium chloride was studied by measuring the heat of mixing ΔHmix of a supercritical gas with the liquid phase. The measurements were carried out using a new customized mixing unit developed for an isothermal differential heat flux calorimeter Setaram BT 2.15D. The experimental technique was specifically adapted for measurements with acid gases (H2S, CO2) in water and salt solutions. The heats of mixing were measured at temperatures of 323.1–373.1 K, and at pressures up to 20 MPa in the regions where the solution is unsaturated and saturated by gas. The concentration dependence of ΔHmix allowed to derive simultaneously the limiting enthalpy of solution ΔHsol and the gas solubility limit. The influence of temperature, pressure and salt concentration (up to 3 molal) on the solubility limits and on the enthalpies of solution was examined. The salting out effect, as measured by Setchenov constant, does not vary strongly with the temperature, pressure, or electrolyte concentration. The consistency between our results and literature data was verified. The reasonable agreement suggests that this technique, beside being a reliable source of enthalpy data, is also suitable for the indirect determination of gas solubility limits.